Display panel or portion thereof with a graphical user interface



FIG. 1 is a front view of a display panel or portion thereof with a graphical user interface showing a first embodiment of our design; and,

FIG. 2 is a front view of a display panel or portion thereof with a graphical user interface showing a second embodiment thereof.

The outermost broken line rectangle illustrates a display panel or portion thereof that forms no part of the claimed design. 

CLAIM The ornamental design for a display panel or portion thereof with a graphical user interface, as shown and described. 